What is a Co-Witness Mount?

Co-witness refers to the alignment of your iron sights with your optic sights. The basic concept is when aiming down sights you would expect both your iron sights and optic sights to be aligned which is co-witness. The two most comment types of co-witness are absolute co-witness and low 1/3 co-witness.

Absolute co-witness is having your optic is mounted at the same height as the iron sights. When looking through the iron sights and optic sights, the crosshairs on the optic sights are aligned with the iron sights.

Lower 1/3 co-witness is having your optic mounted slightly higher than the iron sights. When looking through the optic sight the, the irons sight are lower than your crosshair of the optic sight. The Iron sights appear in the lower 1/3 of the optics FOV. Dropping your sight to look through the iron sights, the crosshair will align with the iron sights.

Lower 1/3 Co-witness Pros: Extra height allows you to see over fixed sights allowing an uncluttered view through optic sights.

Lower 1/3 Co-witness Cons: Must raise or lower line of sight when switching between optic or iron sights.